Configuration management support is implemented by means of protocols defined in standards other than the DICOM standard. These protocols are described here in terms of actors, transactions, and profiles.
Actors are analogous to the Application Entities used within the DICOM profile. An actor is a collection of hardware and software processes that perform a particular role. When a device provides or uses a service it will include an actor to handle the relevant network activity. DICOM Configuration actors may co-exist with other Application Entities on a device. Some DICOM Configuration actors exist as parts of general use IT equipment. Like the Application Entity, specification of an Actor does not imply anything about the details of the actual implementation.
The actor interactions are defined in terms of Transactions. Each transaction is given a name. The transaction may in turn comprise a variety of activity. All transactions are defined in terms of actors that are communicating. The relationships between actors in a transaction may be more complex than the simple SCU and SCP roles in DICOM activities. When the transaction includes interactions with a person, the transactions may be implemented by user interfaces, removable media. and other mechanisms. The person is described in terms of being an actor from the perspective of the transaction use case model. More typically the transactions are a series of network activities that perform a specific operation.
A transaction includes both mandatory and optional components. An Actor that is implementing a transaction is required to implement all of the mandatory components.
Some transactions include human actors in the transaction definition. These actors are not defined as actors elsewhere, nor are they included in profile descriptions. They exist to specify that some sort of mechanism must be provided to permit these people to interact with the computer actor. Other details of how that user interface is provided are not specified by this standard. For an example, see the definition of the Configure DHCP transaction.
Conformance is further managed by means of Profiles. A Profile is defined in terms of what transactions are required for an actor and what transactions are optional. An implementation of a specific actor is documented by specifying what optional transactions and transaction components have been implemented. An implementation that omits any required transactions or components cannot claim to be an implementation of that Actor.
For example, in the Network Address Management Profile the DHCP Server is required to perform the three Transactions to configure the DHCP server, find and use DHCP servers, and maintain the DHCP leases. It may also support the transaction to update the DNS server by means of DDNS coordination.
A Profile includes definitions for more than one Actor. It specifies the transactions for all of the actors that cooperate to perform a function. For example, the Network Address Management Profile covers the DHCP Server actor, the DHCP client Actor, and the DNS Server actor. There must be at least one DHCP Server and one DHCP Client for the system to be useful. The DNS Server itself is optional because the DHCP Server need not implement the DDNS Coordination transaction. If the DNS Server is part of the system, the DDNS coordination is required and the DHCP Server will be expected to participate in the DDNS Coordination transaction.
Note: There may be a DNS server present on the same network as a DHCP Server, but if it is not providing the DNS Server actor from this profile it is not part of the DICOM Configuration activities.
The profiles, actors, and transactions are summarized in the following sections. The detailed description of actor and transactions for each specific profile are described in annexes for each profile. The transactions are documented in terms of parameters and terms from their original standards document, e.g. an RFC for Internet protocols. The full details of the transaction are not described in the annex, only particular details that are relevant to the DICOM application of that transaction. The complete details for these external protocols are documented in the relevant standards documents for the external protocols. Compliance with the requirements of a particular profile shall include compliance with these external protocol documents.
The DHCP Server is a computer/software feature that is provided with a network configuration description, and that provides startup configuration services in accordance with the DHCP protocol.
The DHCP Client is a software feature that is used to obtain TCP/IP parameters during the startup of a computer. It continues operation to maintain validity of these parameters.
The DNS server is a computer/software feature that provides IP related information in response to queries from clients utilizing the DNS protocol. It is a part of a federated database facility that maintains the current database relating machine names to IP address information. The DNS server may also be isolated from the worldwide federated database and provide only local DNS services.
The DNS client as a computer/software feature that utilizes the DNS protocols to obtain IP information when given hostnames. The hostnames may be in configuration files or other files instead of explicit IP addresses. The hostnames are converted into IP addresses dynamically when necessary. The DNS client uses a DNS server to provide the necessary information.
The NTP server is a computer/software feature that provides time services in accordance with the NTP or SNTP protocol.
The NTP client is software that obtains time information from an NTP server and maintains the client time in synchronization with the time signals from the NTP server.
The SNTP client is software that obtains time information from an NTP server and maintains the client time in approximate synchronization with time signals from the NTP server. The SNTP client synchronization is not maintained with the accuracy or precision that NTP provides.
The LDAP server is a computer/ software feature that maintains an internal database of various directory information. Some of this directory information corresponds to DICOM Configuration schema. The LDAP server provides network access to read and update the directory information. The LDAP server provides a mechanism for external loading, unloading, and backup of directory information. The LDAP server may be part of a federated network of servers that provides a coordinated view of a federated directory database in accordance with the rules of the LDAP protocols.
The LDAP client utilizes the LDAP protocol to make queries to an LDAP server. The LDAP server maintains a database and responds to these queries based on the contents of this database.
The following transactions are used to provide communications between actors in accordance with one or more of the DICOM Configuration protocols.
Configure DHCP Server
This transaction changes the configuration on a DHCP server to reflect additions, deletions, and changes to the IP parameters that have been established for this network.
Find and Use DHCP Server
This transaction is a sequence of network messages that comply with the rules of the DHCP protocol. It allows a DHCP client to find available DHCP servers and select the server appropriate for that client. This transaction obtains the mandatory IP parameter information from the DHCP server and obtains additional optional parameters from the DHCP server.
The service staff uses this transaction to set the initial configuration for a client.
This transaction deals with how the DHCP client should behave when its IP lease is not renewed.
This transaction documents whether the DHCP server is coordinating with a DNS server so that access to the DHCP client can be maintained using the hostname assigned to the DHCP client.
This transaction obtains the IP address for a computer when given a hostname.
These transactions are the activities needed for an NTP or SNTP client to maintain time synchronization with a master time service.
Find NTP Server
This transaction is the autodiscovery procedure defined for NTP. This may use either a broadcast method or a DHCP supported method.
Find LDAP Server
In this transaction the DNS server is queried to obtain the IP address, port, and name of the LDAP server.
Query LDAP Server
In this transaction the LDAP server is queried regarding contents of the LDAP database.
Client Update LDAP Server
This transaction updates the configuration database using LDAP update instructions from the client being configured.
Maintain LDAP Server
This transaction updates the configuration database using local services of the LDAP server.
Figure 7.1-1 shows the actors and their transactions. The usual device will have an NTP Client, DHCP Client, and LDAP client in addition to the other applications actors. The transactions “Configure DHCP Server”, “Configure Client”, and “Maintain LDAP Server” are not shown because these transactions are between a software actor and a human actor. DICOM does not specify the means or user interface. It only requires that certain capabilities be supported.
Figure 7.1- 1 Transactions and Actors